44 Journal of the Mitchell Society [December 



forms. These critical temperatures are of great economic importance 

 in the control of insects of stored products and hundreds of thousands 

 of dollars worth of furs are now held at low temperatures during the 

 summer months thus avoiding attacks of moths. While, at the other 

 end of the temperature scale, we find many of our largest flour mills 

 provided with special heating apparatus so that the temperature of 

 the mill may be raised beyond the critical point for mill insects. When 

 it is remembered that temperature is intimately related to humidity 

 and other factors it is perceived that the problem is an exceedingly 

 complex one and one that will have to await better facilities for con- 

 trolling these factors than any as yet available. Perhaps the most 

 interesting single bit of information as yet gleaned from the many im- 

 portant ones relative to the temperature factor is the knowledge that 

 certain species of plant lice will withstand a much lower temperature 

 than their parasites. Hence they are able to survive and continue to 

 l)reed in cool weather whereas the development of the parasites is 

 checked, thus the plant lice gains the upperhand of their parasites and 

 do widespread damage to crops during cool weather, but if the weather 

 is warm the parasites gain the upper hand and keep the plant lice in 

 check. 



Humidity is perhaps next to temperature, the most important 

 single factor in the ecological relations of insects. Here again we have 

 practically an unexplored field and outside of the knowledge that many 

 insects require a relatively high humidity for their best development, 

 our knowledge is rather limited. The fact that air passed through 

 certain strengths of various salt solutions and solutions of certain acids 

 can be given almost any percentage of humidity required is of great 

 service to the entomologist and opens up a fertile but practically un- 

 touched field. 



In addition to the above problems of the ecological factors, which 

 may be called laboratory ecology, there is another realm to which I 

 desired to call your attention namely, field ecology. In field ecology 

 we are not concerned with the individual factors but with the environ- 

 ment as a whole. In other words we take our selected area as we find 

 it in nature and try to analyze it by determining the dominant species 

 and then determine the reasons for their dominance. The whole of 

 economic entomology may be said to belong to the field ecology of in- 

 sects but field ecology of insects is broader than economic entomology 

 for it is concerned not only with economic forms but with others as 

 well. 



